The present invention relates to binders and more particularly to plastic binders for holding notes, price lists, and other written materials.
Binders, which are commonly used in business and education, often have operable rings for holding pages and sometimes include pockets for holding writing instruments and other objects. A typical binder includes interior and exterior vinyl cover sheets joined by heat sealing. Cardboard stiffening sheets between the cover sheets can impart some rigidity and plastic foam padding can be included as well.
Generally, the binder includes front and back cover panels separated by one or more hinged panels and, in some cases, a relatively rigid spine panel. A pliable closure panel that extends from one of the cover panels can also be included. Usually the cover sheets are fused together by heat sealing along the periphery of the binder. Some binders are provided with an additional transparent plastic pocket sheet that is heat sealed to the interior cover sheet. Pockets, such as sleeves for writing instruments and the like, can be formed by this additional sheet.
Heat sealing is performed using an electrostatic die. A conventional die is provided with electrically heated brass bars or projections so arranged that they contact the portions of the vinyl sheets to be heat sealed. Excess material extending from the fused edges is torn off, forming a "tear seal".
Conventional vinyl binders are provided with heat sealed strips extending along hinge areas and closure flaps to impart flexibility so that the binder can be easily opened or closed. The heat sealing process causes the melted plastic to flow, leaving thinner material in the heat sealed areas. Thus, the binder tends to fold and ultimately crack in these heat sealed areas. Often the area in which folding takes place as a binder is opened and closed is no more than 1/8 of an inch wide.
It is sometimes found that heat sealed strips along the spine of the binder that permit sufficient flexibility also permit the cover panels to "wobble" in relation to the spine. Another drawback of conventional binders is that the provision for holding a writing instrument is often unsatisfactory because thin pens and pencils tend to fall out. Also a loop provided for the purpose of holding a writing instrument will somes times interfere when opening or closing the binder. The formation of these loops often requires an additional manufacturing step.